This invention relates to apparatus and methods for automatically monitoring and evaluating manufacturing processes, and goods made by manufacturing processes. The invention relates to, for example, operations which produce an ongoing stream of outputs such as discrete absorbent articles, for example disposable diapers, effective to absorb body fluids. Such absorbent article products are typically fabricated as a sequence of work pieces being processed on a continuous web, typically operating on a processing line. Such absorbent article product generally comprises an absorbent core confined between a moisture impervious baffle of e.g. polyethylene and a moisture pervious body side liner of e.g. non-woven fibrous material. The absorbent articles are typically made by advancing one of the webs along a longitudinally extending path, applying the absorbent core to a first one of the webs, and then applying the second web over the combination of the first web and the absorbent core. Other elements such as elastics, leg cuffs, containment flaps, waste bands, and the like are added as desired for the particular product being manufactured, either before, during, or after, applying the second web. Such elements may be oriented longitudinally along the path, or transverse to the path, or may be orientation neutral.
Typically, such manufacturing processes are designed to operate at steady state at a pre-determined set of operating conditions. While such process is operating at steady state conditions, the result desired from the process is desirably and typically achieved. For example, where the process is designed to produce a certain manufactured good, acceptable manufactured goods are normally produced when the process is operating at specified steady state conditions.
As used herein. “steady state conditions” represents more than a single specific set of process conditions. Rather, “steady state” represents a range of specified process conditions which correspond with a high probability that acceptable goods will be produced, namely that the products produced will correspond with specified product parameters.
While a conventional such process is operating, sensors and other monitoring apparatus are typically used individually at various locations along the processing line to automatically sense various respective parameters with respect to, and to otherwise monitor the condition of, the good being manufactured. For example, in a diaper manufacturing operation, a sensor such as a photoelectric eye can be used to sense the presence or absence of a particular element of the diaper such as an ear, the edges of a waist band, the edge or edges of the absorbent core, or the like. In addition, a vision imaging system can be used as another form of sensor to collect and record visual images of, as well as to make measurements on, the units of goods being manufactured.
Known analytical models and control models are based on assumptions that errors related to such sensings, collectings, and recordings are negligible, and thus that all determination signals, or absence of such determination signals, including quantitative signals, as well as the visual images and image analysis measurements made therefrom, are in fact accurate representations of the elements purportedly being detected and/or measured.
However, actual operation of many manufacturing processes, including highly automated processes, typically includes the occurrence of periodic, and in some cases numerous, errors, inaccuracies, or omissions in the determination signals and/or the visual images. Such errors, inaccuracies, or omissions may be caused by any of a variety of factors. Such factors may be, for example and without limitation, complete catastrophic failure of the sensor, intermittent failure of the sensor, error in sensor calibration, a transient out-of-calibration condition of the sensor, an effective obstruction between the sensor and the element to be sensed, or a loose or broken connection between the sensor and the computer or other controller to which the sensor is connected. Such factors also generally apply to vision imaging systems, including the lighting or camera, as well as numerous product component and process irregularities.
A variety of possible events in the manufacturing operation can cause the production of units of product which fall outside the specification range. For example, referring to manufacture of absorbent articles, stretchable materials can be stretched less than, or more than, the desired amount. Elements can become misaligned relative to correct machine direction and/or cross-machine direction registration in the manufacturing operation, or improperly folded over, or creased, or crimped, or torn. Timing between process steps, or speed of advance of an element, can stray from target ranges. If non-catastrophic changes in process conditions can be detected quickly enough, preferably process corrections can be made, and the variances from target conditions can accordingly be controlled such that the product remains within accepted specification ranges, without having to shut down the manufacturing operation, and preferably without having to cull, and thereby waste, product.
A variety of automatic product inspection systems are available for carrying out routine ongoing automatic inspection of product being produced on a manufacturing line, and for periodically and automatically taking samples for back-up manual evaluation. Indeed, periodic manual inspection and evaluation of product samples is still important as a final assurance that quality product is being produced. However, in high-speed manufacturing processes, the primary tool for ongoing real-time product inspection is one or more computer controlled automatic inspection systems which automatically, namely without necessary direct human intervention, inspect the product being manufactured, preferably inspecting every unit of such product.
Where product is outside the accepted specification range, and should be culled, it is desired to cull all defective product, but only that product which is in fact defective. If too little product is culled, or if the wrong product is culled, then defective product is inappropriately released for shipment. On the other hand, if product which in fact meets accepted product specification is culled, then acceptable and highly valuable product is being wasted.
Body-fluid-absorbing absorbent articles such as are of interest herein for implementing the invention are typically manufactured at speeds of about 50 to about 1200 articles per minute on a given manufacturing line. Accordingly, if each unit of product is to be inspected, as here desired, the inspection process must be fast, in order to keep up with the rate of product manufacture here contemplated. Especially at the higher speeds suggested here, it is physically impossible for a typical operator to manually inspect each and every absorbent article so produced. If the operator reacts conservatively, culling product every time he/she has a suspicion, but no solid evidence, that some product may not meet specification, then a significant amount of in-fact-good product will have been culled, and thereby wasted. By contrast, if the operator takes action only when a defect has been confirmed using visual or other manual inspection, defective product may have already been released for shipment before the defective condition has been confirmed.
One way for the operator to inspect the product for conformity with the specification range is for the operator to periodically gather samples of the product being produced, and to inspect such samples off-line. In the manufacture of absorbent articles of particular interest to the inventors herein, such off-line inspection is conventionally practiced by placing the physical product sample on a light table, stretching the product out to its full length and width, and taking desired measurements. Based on the measurements taken, the operator then determines any suitable process adjustments, and implements the respective adjustments.
Random inspections stand little prospect of detecting temporary out-of-specification conditions. On the other hand, where samples are taken by an operator in response to a suspected out-of-specification condition, given the high rate of speed at which such articles are manufactured, by the time the operator completes the inspection, the suspected offensive condition may have existed long enough that a substantial quantity of questionable or defective product will have either been shipped or culled without the operator having any solid basis on which to make the ship/cull decision. Further, automated manufacturing process controls may have self-corrected the defect condition before the operator can take samples, or before the operator can complete the visual/physical inspection and act on the results of such visual inspection. Thus, conventional manual inspection by an operator, while providing the highest potential level of inspection quality holds little prospect of effectively monitoring and controlling temporary out-of-specification conditions, or of pro-actively controlling processing conditions which could produce out-of-specification product, in processes fabricating product at the above-specified rates.
While off-line inspection can be a primary determinant of quality, and typically defines the final quality and disposition of groups of the product, on-line inspection, and off-line evaluation of on-line-collected data, typically associated with certain manufacturing events, may provide valuable insight into both the operational characteristics of the manufacturing process and the final quality parameters of the product, as well as insight into potential proactive improvements which might be made in process control.
Thus, in processes that operate at speeds such that manual inspection of each unit of product is an unrealistic expectation, the primary mechanism for inspecting each unit of product is a computer controlled automatic inspection and control system, optionally including a vision imaging system, backed up by periodic manual inspections of physical samples, or sample images, of product to confirm the accuracy of the decisions being made by the automatic inspection and control system. Such automatic inspection and control system automatically, namely without necessary direct human intervention, inspects the product being manufactured, preferably inspecting each and every unit of such product.
Automatic inspection and control systems rely on a plurality of sensing devices and analytical tools to detect a corresponding plurality of different pre-selected parameters, qualitatively and typically quantitatively, in the goods being produced. Such pre-selected parameters are selected for their prospects of representing the actual overall degree to which the goods conform to pre-selected specifications. The conclusions reached, and the control actions taken on the basis of such conclusions, are only as reliable as the design and implementation of the automatic inspection system, and the accuracy of the determination signals created and/or developed by the respective sensing devices and analytical tools. The reliability of such determination signals is thus critical to the ability of the automatic inspection and control system to sufficiently and efficiently control the manufacturing operation.
While sensors and analytical tools are readily available for use in automatic inspection and control systems, typical such sensors and analytical tools must be carefully manipulated, such as positioned, mounted, calibrated, programmed, and the like, and so maintained in a manufacturing environment.
As a practical matter, such sensors and tools will periodically develop and/or transmit erroneous determination signals, even when managed by a regular maintenance program. In typical situations, the inspection and control system is unable to detect the fact that such signals are erroneous signals, whereby the inspection and control system fails by responding, erroneously, as though the signals were in fact accurate or fails by not responding at all. While the overall purpose of automatic inspection and control is to minimize shipment of defective product, such erroneous response can in fact result in the control system being the cause of product being out-of-specification. Namely, an error in the control system can actually result in release and shipment of product which does not meet accepted specification ranges. So it is critical that the incidence of errors, particularly erroneous determination signals, be limited as much as possible.
As used herein, “erroneous signals” includes signal changes which result from changes in the substrate or other material being sensed by the sensor or tool. For example, if the current supply of the material being sensed has greater or lower opacity than the material for which the sensor or tool is calibrated, then the received signal can give an erroneous indication of the condition of the goods. In such case, and where the inappropriate signal persists, the sensor or tool is preferably recalibrated and/or its sensitivity is adjusted.
As suggested above, there are both advantages and limitations to automatic inspection and control systems. A significant advantage of such systems is that the speed of automatic analysis enables such systems to inspect up to as many as each and every unit being fabricated on manufacturing lines operating at the suggested speeds. Such automatic inspection and control systems are required where rate of product manufacture exceeds the rate of reasonable human/manual inspection.
A limitation of automatic inspection and control systems is that, while such systems conventionally may have the ability to distinguish an accurate determination signal from an erroneous determination signal, they cannot compare, correct, or compensate for, erroneous signals. Further, conventional such systems inspect only a limited portion of the product. And while erroneous signals and readings do not happen often enough to suggest that such automatic inspection and control systems have no net value, to the extent the incidence of erroneous signals can be reduced, or to the extent the incidence of accepting erroneous signals as accurate representations of the overall condition of the product can be reduced, the value of such automatic inspection and control systems will be enhanced.
Where a stream of products is fabricated from a continuous web of substrate material, and wherein a number of elements are established on the substrate web as the web traverses the length of the manufacturing line, it is important that the elements be registered with both the machine direction and the cross-machine direction of the substrate web.
Where elements are to be established on e.g. a substrate web, deviation from proper cross-machine direction registration can result from a deviation of the substrate web or a deviation of the respective element on the web. While a correction of either the web or the element can correct the relative positioning of the element with respect to the web, if the component adjusted was in fact in correct registration with the machines in the manufacturing line before adjustment, the result is that both the adjusted component and the non-adjusted component are then out of registration with the cross-direction alignment of the machines on the manufacturing line. Where more than two components are involved, such correction which takes an additional component, namely the component changed, out of registration with the machines, can also take the additional component out of registration with one or more of the other components.
As an hypothetical example, suppose components 1, 2, and 3 are assembled in a work piece. Components 1 and 2 are out of cross-machine direction registration with respect to each other. Components 1 and 3 are in fact in cross-machine direction registration with the machines and are in proper cross-machine registration with each other. Component 2 is thus out of registration with components 1 and 3 and out of registration with the machines. For purposes of this hypothetical example, the operator notes that components 1 and 2 are out of registration with respect to each other. If the operator adjusts component 2 to component 1, the adjustment works well. If, on the other hand, the operator adjusts component 1 into correct cross-machine direction alignment with component 2, the misalignment of component 2 will not have been corrected, and component 1 will have been taken out of alignment with respect to component 3 and the machines. Where several components are involved, the corresponding several work stations, where the components are established or operations are performed on the work pieces, are potential locations on the manufacturing line for cross-direction alignment adjustments. Thus, several work stations along the manufacturing line provide separate and distinct opportunities for cross-machine adjustment of at least one component, in addition to opportunity for adjustment of the substrate web.
Using current technology, the operator has little basis on which to decide which of the respective components is actually out of cross-direction alignment and/or why. Accordingly, the operator will actually guess which component to adjust, and/or what other corrective action to take without having sufficient technical data to confirm that the decision made is the best decision, or even an appropriate decision. Should the operator guess incorrectly and thus act incorrectly, the result can be to cause relative misalignment of one or more additional components. Further, every time misalignment is found, there is potential for adjusting alignment of the base web. Where alignment of the base web is adjusted improperly, all the components on the web should be adjusted in order that such components not be out of alignment with the substrate web. Each such misalignment of the web provides its own arc in a relatively zig-zag, or snake-like, path along the manufacturing line, rather than the desired path of the substrate web proceeding along a given single plane of advance.
It is an object of this invention to provide improved inspection and control systems, and corresponding methods of measuring cross-direction parameters of the work pieces, which provide improved basis for determining which of the components is misaligned.
It is another object of this invention to provide improved inspection and control systems, and methods of measuring parameters of the product so as to increase reliability of the determination signals created and/or developed by such inspection and control systems.
It is still another object of this invention to provide improved inspection and control systems which evaluate cross-direction position of the respective component with respect to an established reference line, such as a manufacturing path centerline, based on the positions of the machines in the line of manufacturing machines.
It is yet another object to provide for adjusting and/or otherwise correcting the manufacturing process according to deviation from a target specification.
Still another object is to provide inspection and control systems including vision imaging systems establishing the cross-direction positions, with respect to the line of manufacturing machines, of respective components on the work pieces.
Yet another object is to provide such inspection and control systems, the vision imaging systems having suitable system logic capable of calculating corrective action based on a number of measurements taken from representation of a fully digitized image of a work piece on the manufacturing line.
A further object is to provide such inspection and control systems, including vision imaging systems connected to proper control devices such that the inspection and control system automatically makes proper cross-direction adjustment in the manufacturing line to bring the component back toward correct relationship with the reference line.
It is yet another object to provide an inspection and control system wherein the control system interacts with a human operator in determining cross-direction out-of-specification condition, and calculates corrective action to be taken.
It is still another object to provide inspection and control systems which capture digitized full visual images of respective work pieces and, with or without interaction with an operator, inspect the respective visual images for presence and proper positioning of a plurality of components on the work piece.
It is a further object to provide improved inspection and control systems which interact with an operator, leading the operator through a series of computer-aided measurements.
Still another object is to provide inspection and control systems which calculate responses based on the operator's series of computer-aided measurements, and wherein either the operator or the inspection and control system can implement the calculated responses.
Yet another object is to provide inspection and control systems which capture and store digitized full visual images of respective work pieces, and retrieve the full visual images for off-line analysis.